2023-09-20_BONDING - M1980047 - Laserfiche WebLink

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Colony Reclamation Cost Estimate, Update to Exhibit L Rev. Sept. 2023 were to be backfilled at an angle close to repose. Further, as stated on Page E-49 of the original permit application, "other appropriate measures" are anticipated here because this area "will consist of exposed bedrock and probably (is) not amenable to direct topsoiling." Similar to the rock slopes above and below the access roadways that were released in the 2007 Partial Acreage Release AR-01, no reclamation costs for the bare rock areas downstream of the cofferdam are therefore included in this estimate. In the final paragraph of the section dealing with "Dams" on Page E-48 of the original permit application, it states that "Upon abandonment the dams will be removed unless agreement is made with another party to utilize and assume responsibility for them. This approach was approved for Middle Fork Dam in the 2007 Partial Acreage Release AR- 01, and in view of the above discussion a similar approach for the Davis Gulch Cofferdam is the base case for this bond calculation. Accordingly, no reclamation costs are included for Area 9. Davis Dam Materials Stockpile, Area 10B This 10 acre area contains a stockpile of rock excavated from the Davis Gulch Dam site to store materials produced in clearing the dam foundation to be used later as rockfill for the dam's outer shell. It contains approximately 575,000 cy of miscellaneous rock materials, that in 1982 were intended to be used to construct the full size Davis Gulch Dam in 1982. It is unlikely that dam will be built as an earth and rockfill dam. If a dam is built in Davis Gulch, it will probably use the Roller Compacted Concrete technology that was used for Middle Fork Dam in 1984. Consequently, this stockpile will need to be removed and the exposed footprint regarded, topsoiled and seeded. The best location to relocate this material is the nearby Coarse Ore Gulch where it can be hauled and laid up against the valley walls at a relatively mild slopes until the materials stockpile is exhausted. The relocated stockpile materials placed in Coarse Ore Valley would then be topsoiled and revegetated. Once the rockfill stockpile has been exhausted, the underlying soils will be ripped in place and revegetated with the seed mix in Table E-6 on page E-42 of the 1980 permit application. The underlying soil materials will need to be ripped to a depth of 2 feet before re-seeding Some topsoil from the Upper Davis Gulch Topsoil Pile (Area 10D) may also be used here if the materials under the rock stockpile are not deemed suitable to sustain the revegetation. The footprint of the rock stockpile will then be revegetated with the seed mix in Table E-6 on Page E-42. The topsoil stockpile planned for this area would come from the nearby Upper Davis Gulch Topsoil Pile (Area 10D) until it is exhausted as needed to cover the 10 acres of this stockpile's footprint It should be noted that this pile does not impede flows in Upper Davis Gulch, and the channel around it was rip-rapped and slush grouted in the mid 1980s. The channel is stable. The presence of this stockpile does provide a good sediment trap from upstream flows and thereby reduces sediment load to the Davis Gulch Dam immediately downstream. The small reservoir impounded by the Davis Gulch Dam is currently used as a source of water for dust suppression on the plateau roads, and the sediment reduction due to this stockpile reduces the dredging needs for that pond. Finally, it serves as a convenient watering pond for livestock and wildlife in the area. At some future date it might be worth considering leaving this stockpile and its hardened channel Page 9